is entire in \(\lambda .\) 
Using the standard estimate (see [1]})
\(|\sin \rho l| \ge M^{-1} e^{|\mathrm {Im}\, \rho |l}, \quad |\rho | = \frac{\pi (n+\frac{1}{2})}{l}, \; n \in \mathbb {N}, \; n \ge N^*,\) 
